Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers are thin strands of glass capable of transmitting the signals over long distances with very low loss.
Optical networks often employ wavelength division multiplexing (WDM) to increase transmission capacity. In a WDM network, a number of optical channels are carried in each fiber at disparate wavelengths. Network capacity is increased as a multiple of the number of wavelengths, or channels, in each fiber.
In order to process encoded data, individual optical channels must be dropped or removed from the WDM signal for individual processing. Tunable filters provide one means of passing an individual channel while rejecting the other channels in a WDM signal. However, tunable filters may drift due to environmental instabilities resulting in inaccurate tuning.